1. Field of the Invention
This invention relates to homo- and copolymers of (meth)acrylamide compounds.
2. Description of Current Problems
High molecular weight polymers based on (meth)acrylamides are known flocculants, which are used, for example, in waste water clarification and in the removal of water from sludge and sewage treatment plants or to remove water from coal slurries. The polyacrylamides may be commercially obtained in solid form, in aqueous solution, or as water-in-oil polymer emulsions. Although these polyacrylamides are excellent flocculants, there are problems handling these polymers. For example, standard commercial aqueous solutions of high molecular weight polyacrylamides, which are prepared through the polymerization of acrylamide in an aqueous solution, have a very high viscosity--even at a polymer content of only 5 percent--so that high transport costs relative to the polymer are incurred when such solutions are shipped.
Water-in-oil polymer emulsions of polyacrylamides can be quickly dissolved in water by inverting the water-in-oil emulsion in the presence of wetting agents as taught by German Pat. No. 2 154 081, however, then in addition to the flocculant the hydrocarbon oil from the water-in-oil polymer emulsion goes into the waste water and can no longer be removed therefrom by simple means.
British Pat. No. 1,397,933 teaches the dispersion of finely divided water-soluble polymers, for example, polyacrylamide or polyacrylic acid having a particle diameter less than 0.1 mm in a nonaqueous organic medium such as gasoline or a chlorinated hydrocarbon and further teaches the addition of at least one surfactant and, in some cases, anti-foaming agent to the resulting dispersion. When the dispersion is mixed with water, dilute aqueous polymer solutions result. These contain the organic phase of the original polymer dispersion.
German OS No. 29 24 663 relates to a process for the preparation of an aqueous dispersion through the polymerization of (meth)acrylamides or (meth)acrylic acid in an aqueous solution of a water-soluble polymer such as polyethylene glycol, polyvinyl alcohol, polyethylenimine, polyvinylpyrrolidone or soluble starch. The viscosity of these primary dispersions is relatively high, which leads to problems in using the polymer.
Solid polyacrylamides are slow to dissolve in water, so that relatively long dilution times are required to prepare dilute aqueous solutions of high molcular weight polyacrylamides from the solid products. Solid polyacrylamides frequently contain relatively large amounts of very fine particles less than 0.3 mm in size. In order to obtain largely dust-free products, the solid products are screened. However, the finely powdered products cause problems when they are used, because they have a high tendency to generate dust and when the user tries to make dilute aqueous solutions from them, they cause especially serious problems since the fine particle fractions frequently float on the surface of the water and clump together rather than forming a homogeneous solution.
The present invention relates to the desire to be able to provide homo- and copolymers of (meth)acrylamide compounds in a fine particle form, which has a tendency to generate dust, in a form which permits dilute aqueous solutions to be prepared in a simple manner. Another desired feature is to provide preparations of the above-cited water-soluble polymers which can be used as flocculants and which have the lowest possible viscosity.